在使用DHTML进行编程时比较有用，防止浏览器在请求中，死掉

var  xml  =  GenXMLData(tableName, fieldID,  "" ,  "" );
     var  content  =   " < table height=100% width=100%><tr><td><div id='divDoing' style ='position:absolute; left:500px; top:136px; width:196px; height:105px; z- index:1;'><div align='center'><p><img src='../Images/doing.gif' width ='32' height='32'/></p><p><br/>正在查询、请稍候……</p> </div></div></td></tr></table> " ;
    contentTD.innerHTML  =  content;
         var  XmlHttp = new  ActiveXObject( " Microsoft.XMLHTTP " );
    XmlHttp.onreadystatechange = function () {
        if (XmlHttp.readyState == 4 ) {
             if (XmlHttp.status == 200 )
             {
              contentTD.innerHTML  =  XmlHttp.responseText;
              firstPost  =   true ;
            }
             else
            contentTD.innerHTML  =  content ;
        }
    }
    XmlHttp.open( " post " ,webFile, true );
    XmlHttp.send(xml);